Weed and grass trimmers have been developed which employ a rotatable hub with a short length of flexible nylon or other plastic line extending from the hub. When the hub is rotated (typically at speeds from 6,000 RPM to 12,000 RPM), the tip of the line extending from the hub provides the cutting or trimming action. Grass and weed trimmers using this principle of operation have become popular for their versatility of use and because the flexible trim line is safer to use than rigid rotating steel blades.
Various types of devices have been developed for using such trim lines. Typically, rotating line trimmers or rotating string trimmers employ a line which generally has a circular cross section. The line, in many trimmers, is wound on a storage reel in the hub of the device and is fed out of a hole in the hub in discrete amounts, as the end breaks off or wears off. Trimmers of this type sometimes are referred to as “bump and feed” trimmers, since, when the line breaks off, the bottom of the storage reel is bumped on the ground to cause a spring release of the line within the trimmer, which then plays out a short length of line through a hole in the hub by means of centrifugal force when the trimmer is operating. Typically, the smaller (with 2½″ diameter to 3½″ diameter head) bump and feed string trimmers use relatively small diameter line, normally in the range of 0.065″ to 0.080″ diameter, since the smaller diameter flexible line functions better for the centrifugal feeding of such a smaller diameter bump and feed head.
The reason that small diameter line is used in “bump and feed” string trimmers is that heavier diameter line (for example, 0.115″ to 0.160″ diameter) typically is too stiff for winding and for the centrifugal feeding used in “bump and feed” heads. Commercial bump and feed heads use a larger diameter head than was designed for home use, and operate with somewhat larger diameter flexible line, generally from 0.95″ to 0.105″ diameter and normally have a larger capacity for such line. Thus, less frequent reloading of the line is required.
A problem exists with bump and feed trimmers, however, in that frequently the line which is wound on the storage reel in the hub tends to become stuck, either due to partial fusion of the line within the hub, caused by high frequency vibration, or by successive turns of the line wound on the hub becoming somewhat entangled. As a result, feeding of the line from the hub, when desired, does not always take place. When this occurs, it is necessary to remove the hub from the string trimmer device and manually extract the desired length of line prior to reattaching the hub to the device. This is a very time consuming and frustrating experience for many users of flexible line string trimmers.
For commercial use employing relatively large diameter lines, for example 0.115″ to 0.160″ diameter, fixed-line trimmer heads usually are employed. The large diameter monofilament nylon lines are particularly useful where weed and grass growth is dense. The large diameter lines also provide longer length of service before the line needs to be replaced. Due to the hole design and pattern, smaller standard sized lines (under about 0.095″ diameter) have a tendency to slip out of commercial fixed heads during operation.
One type of fixed line trimmer head for commercial use is the Echo® heavy duty fixed line trimmer head, stock No. 999442-0020. This trimmer head is designed to replace a saw blade trimmer/brush cutter or other types of flexible line trimmer heads. The Echo® trimmer head is open on its underside and provides serpentine paths for the insertion of two fixed lengths of 0.130″ diameter monofilament nylon line. The line is inserted between closely spaced, offset guide surfaces to hold it in place during operation. When a new length of line needs to be inserted, the old line must be removed, and the new line guided in place around the guide surfaces. Because the guide surfaces are close together and 0.130″ diameter line is relatively stiff, it is difficult to install and remove sections of nylon line from the Echo® trimmer head. This difficulty results in excessive time being consumed for the removal and replacement of line segments.
Other approaches to providing trimmer heads using fixed lengths of line are disclosed in the United States patent to Luick U.S. Pat. No. 4,062,114; Jacyno U.S. Pat. No. 4,118,865; and Morabit U.S. Pat. No. 6,314,848. All three of these patents disclose trimmer heads using lengths of line which have an enlarged portion, or an eyelet attached to one end for extension from the inside of the head out through an opening to be held in place by centrifugal force when the head is rotating. When the line is worn or breaks off, it may be removed from the inside by pulling back out in the opposite direction to allow replacement with a new line.
A problem which exists with this type of trimmer head and line combination, however, is that each length of line which is to be used with the head requires a special configuration on the inside end to prevent it from being pulled outwardly through the hole in the head from which the line extends. As a consequence, the cost of the line segments is substantially more than the cost for a line segment made of a piece of line which does not require the additional end configuration, or additional parts to be added to it.
A different approach for utilizing fixed line trimmer heads is disclosed in the United States patent to Moore U.S. Pat. No. 6,401,344. This patent employs a spring-biased clamp supported on the body of the head to engage a line filament, which passes straight through the head to extend outwardly on opposite sides of the head. An actuator button is projected through an opening in the body; and when this button is pressed, the clamp is released so that worn trimmer line may be removed and replaced with a new segment of line. The structure of the internal parts of the head is relatively complex because of the nature of the clamp and the various parts which are used to bias it into engagement with the line, and to allow the release by means of the external button.
Another approach to the utilization of fixed lengths of line for a string trimmer head is shown in the patent to Brandt U.S. Pat. No. 6,347,455. The structure of this patent employs a pair of opposing clamping jaws in the form of spring loaded cams, which are selectively opened by activation of a slide member on the top of the head to allow the insertion of a fixed length of trimmer line, or to allow the removal of a length of trimmer line from an opening on the periphery on the head. The spring loaded cams and the additional slide members again result in a relatively large number of parts causing the manufacture of the head to be somewhat complex and expensive.
Two other U.S. patents which disclose cam operated clamps for holding and releasing line in a string trimmer head are the United States patents to Iacona U.S. Pat. Nos. 5,758,424 and 5,887,348. Both of these patents disclose a trimmer head with a number of access openings about its periphery. Each of the openings is oriented adjacent a cam clamping member which is spring biased to engage trimmer string inserted through the opening. Removal of worn lengths of trimmer line is effected by withdrawing the trimmer line from the inside of the head, moving it in the same direction as it was inserted into the head. Once again, the number of parts which are required to effect the operation disclosed in these patents is relatively high. The cam requires a pivot and an additional spring to bias it into engagement with the line. Assembly of these parts at each of the line openings in the head results in substantial additional manufacturing steps, and additional parts and complexity in the head, thereby causing its cost and potential for failure to increase.
Accordingly, it is an object of this invention to provide an improved fixed line trimmer head for string trimmer machines which overcomes the disadvantages of the prior art, which may be used as an alternative to bump and feed cartridges, which is simple to manufacture, and which facilitates simple and quick loading and replacement of fixed lengths of trimmer line.